In July, the ruling coalition successfully changed a law removing the power of the Supreme Court to strike down government laws on the grounds of 'reasonableness'.

Israel has no written constitution or higher house of parliament, and so this power was seen as a major instrument of the checks and balances the court has on the government.

Israel's Attorney General opposes the government on this issue.

In a sign of how much is riding on today's hearing, all 15 Supreme Court judges will convene to hear the petitions for the first time in Israel's history.

The current government, the most right-wing in Israeli history, believes that the unelected courts have too much power over the elected government and has sought to rebalance the power in its favour.

Removing the 'reasonableness doctrine', which has its roots in the British legal system, was a first step in the government's controversial attempts to reform the judiciary.

The government argues that politicians are appointed by the people, and it is not for judges to decide whether government laws are justified or not.

Earlier this year, the High Court angered prime minister Benjamin Netanyahu by blocking the appointment of a coalition ally to a cabinet position on the grounds that he was unfit to serve as a minister due to past criminal convictions.

Government critics say that the reasonableness measure is one of the few tools the court has to review and scrutinise government decisions.

Weekly mass protests have been taking place throughout the year drawing hundreds of thousands onto the streets in a country of a little over nine million.

The protesters fear that Netanyahu and his allies, many of whom are far-right nationalists, plan to weaken the courts to such an extent that it will result in autocratic rule.

They have been calling for the reforms to be scrapped and Netanyahu to resign.

Although the government argues it is acting on a mandate it was elected to carry out, last week a pro-government demonstration saw an estimated 10,000 turn out in support of the judicial reforms, dramatically smaller than anti-government protests.

The reforms, which are still in motion, have been widely criticised by international allies including the United States; the shekel (Israel's currency) has fallen dramatically against the dollar, investment in the precious tech industry has dropped, thousands of reservists in the Israeli military have threatened to refuse to report for service in protest and Netanyahu's poll ratings have collapsed.

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Retired former top officials in Israel's military and intelligence establishment have also criticised the reforms, arguing that they are harming the country's security and reputation as the Middle East's only democracy.

Scrapping the reasonableness clause was the first phase in an expected series of reforms that include changing the way judges are selected and ending the obligation for a minister to heed the recommendations of their legal advisers - both of which are being seen by opponents as ways of giving the government unchecked power.

The Supreme Court ruling is expected to be delivered at a later, as yet undetermined date, but if they rule against the government, it will pitch Israel into chaos with open warfare between the government and the judiciary.

It's unclear what the consequences will be if the court rules against the government, but it would be the most serious non-military crisis to face Israel.

In one scenario, state bodies like civil servants, the military and intelligence agencies, could be forced to decide whether they follow the court's version of the law, or the government's.

Senior politicians in the coalition have openly said they would ignore the court if it ruled against the government.

In an indication of how the government might react, the Speaker of the Israeli parliament, the Knesset, warned that they "will not acquiesce to its trampling" if the court voted against the government.

He was backed up by Justice Minister Yariv Levin, who has led the government's fight to push through the reforms.

Netanyahu himself hasn't been drawn on whether he would respect or ignore the decision of the court.

However, he did re-post the comments made by the Knesset Speaker which has been seen as an indication he is prepared to defy the court.

Three government ministers though, including defence minister Yoav Gallant, have said the government should respect the court's decision.